Two simple functions to allow better smilies in WordPress. Drop one of them (not both) in your functions.php

Two functions for better smilies in WordPress

/**
 * Filter smilies to allow SVG format with PNG fallback (IE7-IE8)
 * @license   http://www.gnu.org/licenses/gpl-3.0.html
 * @since     1.0.0
 */
add_filter('smilies_src','my_svg_smilies_src', 1, 10);

function my_svg_smilies_src($img_src, $img, $siteurl) {
    $img = rtrim($img, "gif"); // Remove GIF

    if ( strpos( $_SERVER['HTTP_USER_AGENT'], 'MSIE 8' ) || strpos( $_SERVER['HTTP_USER_AGENT'], 'MSIE 7' ) ) {
        $type='png';
    }
    else {
        $type='svg';
    }
    return 'http://domain.com/images/smilies/'.$img.$type.'';
}


/**
 * Filter smilies to allow PNG format
 * @license   http://www.gnu.org/licenses/gpl-3.0.html
 * @since     1.0.0
 */
add_filter('smilies_src','my_png_smilies_src', 1, 10);

function my_png_smilies_src($img_src, $img, $siteurl){
    $img = rtrim($img, "gif");
    return $siteurl.'/images/smilies/'.$img.'png';
}